Studies of chemical metabolism and disposition are designed to provide both applied knowledge in support of chronic toxicity tests conducted by the National Toxicology Program and basic knowledge of those chemical structure and property relationships which determine toxicity. Comparative studies of ethyl carbamate in rats and mice have indicated both species and dose related variations in metabolism and clearance which may account for the reported variations in toxicity. Studies of 2-butoxyethanol indicate that it is readily absorbed and rapidly excreted, but it has a unique pattern of age related hemolytic effects which may be related to its metabolism. An investigation of the sex related variations in sensitivity to the toxic effects of resorcinol indicate that at moderate doses both male and female rats metabolize and clear this compound similarly except for variations in the amounts of two minor metabolites.